Bleaching artificial textile fibers



Patented Mar. 19, 1940 STATES PATNT OFFlE the-Main, Germany,

assignors to Deutsche Gold und Silber Scheideanstalt, Frankfort-on- Ithe-Main, Germany,

many

a corporation of Ger- No Drawing. Application May 1'7, 1938, Serial No.208,495. In Germany May 24, 1937 9 Claims.

This invention relates to a process of bleaching textile fabrics. It isespecially applicable to the continuous bleaching of textile materialsand is especially valuable for the treatment of those textile fibersresulting from manufacturing processes wherein the product is ofcellulosic nature such as artificial staple fibers, artificial silk andsimilar materials. The process utilizes active oxygen yieldingcompounds, more particularly peroxygen compounds such as hydrogenperoxide,

alkali metal percarbonates, alkali metal perborates and other peroxygencompounds.

Previously processes wherein the fiber is first saturated with asolution of hydrogen peroxide followed by squeezing out the excesssolution and drying at elevated temperatures have been restricted in useto the bleaching of animal fibers such as wool. It was generallysupposed that such a process would not be applicable in the 20 bleachingof vegetable fibrous material such as cotton because hydrogen peroxidein contact with such fibers was known to become inactive very rapidly.

We have now discovered that artificial textile 25 fibers fromregenerated cellulose, such as artificial staple fiber, artificial silkformed of a cellulose base, and similar fibrous materials possess amarked accumulating capacity for hydrogen peroxide. On the basis of suchknowledge We have found it possible to bleach fibrous material of thisnature by saturating the fibrous material with the solution of theperoxygen compound (hydrogen peroxide for example) and subsequentlydrying the fibrous material which has previously been freed, ifnecessary, from excess bleaching liquor by a procedure such assqueezing.

The process of the invention may be carried out, for example, bytreating the fibrous mate- 40 rial with the bleaching liquor which maybe a solution of hydrogen peroxide, then treating the fibrous materialwith steam and finally drying that material. Previous to the drying stepthe fabric may be freed, if desired, from excess bleaching liquor bysome procedure such as squeezing or centrifuging the fabric.

During the bleaching stepthe material being bleached should be contactedwith a liquor which is alkaline in reaction. The pH value shouldpreferably be between 7.5 and during the initial phase of the bleaching.Subsequently during the heating and steaming processes the pH value ofthe material being bleached will ordinarily be not more than 8 andpreferably will fall within the pH range 6 to '7 .6 or within thenarrower pH range 6.5 to 7.5. The amount of alkali required during thebleaching process depends on the quantity of alkali or acid contained inor on the fibrous material being bleached, as well as on the type andamount of impurities present in the fibrous material which tend toconsume alkali. The amounts of alkali necessary for bleaching aspecified fibrous material with a given hydrogen peroxide consumption inorder to impart to the material being bleached the desired pI-I duringthe heat treatment can always be readily ascertained by preliminaryexperiments. The saturation or impregnation of the fibrous materialbeing bleached with the activeoxygen yielding solution may also beaccomplished by sprinkling or spraying, such as by conveying thematerial on a moving belt past the spraying device.

We have found that it is most desirable to utilize relatively weakalkalies or salts which yield alkali by hydrolysis. When utilizingstrong alkalies such as caustic soda, especially during continuousoperations, it has been observed that relatively slight excesses ofthese strong alkalies' impart to the material too high a pH value,thereby hindering the bleaching effect. We have therefore foundrelatively weak alkalies to be more desirable for use in our process andespecially prefer to use salts of relatively strong bases and relativelyweak acids such as the alkali metal pyrophosphates, disodium phosphate,borax, alkali metal succinates, alkali metal malonates, and similarsalts. The alkali metal salts of the fatty acids, 1. e., soaps, havealso been found to be especially advantageous since theamount added neednot be determined with considerable exactitude since their total alkalicontent is relatively small. Fibrous material is also favorablyinfluenced by the presence of soap, it being observed that a softer feelis thereby imparted thereto. be advantageously'adjusted so that thedesired pH value is obtained by using a buffer mixture such as, e. g., amixture of NaOH and monopotassium phosphate, or a mixture of sodiumcarbonate and sodium bicarbonate. Other buffer mixtures are alsosuitable.

In accordance with one method of proceeding in accordance with ourinvention, the fibrous material to be bleached is first impregnated witha neutral or slightly acid solution, one having a pH below 7.0. Suchneutral or slightly acid solutions are utilized in place of alkalinebleaching solutions. Salts which have the property of raising the pHvalue of, the bleaching solu- The material to be bleached can also 1tion to a value higher than 7.0 are added to the bleach bath, which maycomprise a solution of hydrogen peroxide. Among such salts may bementioned sodium and potassium oxalate.

We have found that a solution containing about 5 cc. of 40% (by volume)hydrogen peroxide solution and 5 grams of sodium oxalate per liter willhave a pH value of approximately 6.6 at 20 C. At 100 C. the samesolution, due to hydrolysis of the salt, will have a pH value ofapproximately 9.0. By using neutral or slightly acid bleaching solutionsduring the step wherein the textile material to be bleached isimpregnated with the solution there has been found to occur no importantloss of hydrogen peroxide even upon prolonged standing. However, at theelevated temperature, due to hydrolysis, the desired alkalinity forrapid bleaching is secured.

We have found that from 3 to 15 cc. of hydrogen peroxide solution (40%by volume) per liter provides the best bleaching bath. The consumptionof hydrogen peroxide for each 100 grams of material being bleached willbe-found to amount to from 0.3 to 1.5 cc. of hydrogen peroxide solution.

The amounts of bleaching agent and the total alkali content present areso controlled that the material being bleached at the conclusion of theheat treatment contained substantially no undecomposed peroxide. Byregulating the temperature of drying and the pH of the goods during theheat treatment or drying step it is possible to regulate the speed ofactive oxygen evolution so that the process occurs either rapidly orslowly, thus carrying out the reaction in such a manner that thefinished product contains no undecomposed peroxide. The steaming of thematerial being bleached is preferably carried out at temperatures ofapproximately 100 C.

After-treatment of the textile goods, involving washing and drying, maybe eliminated, particularly if the bleaching is carried out so that thematerial being bleached is substantially free from hydrogen peroxide atthe completion of the heat treatment step. The steam treatment may alsobe eliminated, the steaming being replaced by a drying process. It hasproven advantageous under these conditions to dry the material which hasbeen preliminarily impregnated with the bleaching liquor, first, atrelatively high temperatures, followed by drying at relatively lowtemperatures.

Drying of the fibrous material, after it has been impregnated with thebleaching liquid, may also be carried out by exposure in the open air atroom temperature. The hydrogen which has accumulated on the fiber exertsa very effective bleaching action during the course of the dryingprocess. In this Way very satisfactorily bleached products are obtained.

The process may also be carried out by drying the fibrous material at anelevated temperature, for example, temperatures within the range to C.,following-the impregnation step. In this case it is observed thatsurprisingly enough a marked bleaching action occurs subsequent to the Vdrying. In carrying out our procedure in accordance with this variationit is recommended that the dried material be subjected to anaftertreatment, for example, by allowing it to stand in the air at roomtemperature (15 to 20 C.). The process may be prolonged, if desired,until all hydrogen peroxide present on the fibrous material iseliminated.

One method of accomplishing our process involves passing the fibrousmaterial continuously through a bath of hydrogen peroxide, then freeingit from excess liquid by centrifuging or squeezing, then treating it forapproximately 10 to 30 minutes with steam, preferably at 100? C., andfinally drying at approximately 50 to C. The material which has beenfreed from excess bleaching liquid'may be immediately subjected todrying, omitting the steam treatment. If this is done the drying shouldfirst be carried out at 90 to C. and subsequently the temperature ofdrying reduced to one within the temperature range 40 to 70 C.

In place of treating the fibrous material with hydrogen peroxide orother peroxygen compound the process may also be carried out by sprayingthe material with the bleaching solution. This is most expedientlyaccomplished by passing the material on a moving band through a sprayingdevice. If desired, the spraying may be repeated one or more times andthe fibrous material may be sprayed on both sides.

In accordance with our invention the ingredients of the bleach bath areso selected that the material being bleached maintains an alkalinereaction, one within the pH'range 7.5 to 10, during the first phase ofthe heat treatment. Subsequently it assumes an approximately neutral orslightly alkaline or acid reaction (pH approximately between 6 to 7.6)during this treatment. The maintenance of these conditions is ofconsiderable importance if good bleaching is to be obtained. The pHvalue of the goods after the steaming or drying treatment is a definitecriterion as to the success or lack of success of the bleach. If theamount of alkaline materials added to the substance being bleached isadjusted so that the material being bleached remains too stronglyalkaline during the entire heat treatment it Will be observed that thebleaching effect is poor and that yellowing may occur.

Determination of the pH of the material may be accomplished as follows:

50 grams of air-dried goods are moistened with 70 cc. of distilledwater. 20 cc. of this liquid is squeezed from the goods. In the case ofsteamed goods enough distilled water is added so that 50 grams ofartificial fiber being bleached contains 70 cc. of liquid. The liquidsqueezed out (20 cc.) is used for the determination of the pH values.This testing method was used in the examples of our improved processwhich will be subsequently described. a

It is possible to employ in the solution of hydrogen peroxide or ofother peroxygen compound used for bleaching purposes special agents suchas emulsions of olein, Turkey red oil, fatty alcohol sulfonates, andother materials which insure softening of the goods and enlivening ofthe bleached color. The process may be continuously carried out incontinuous operations, the impregnation, removal of excess liquor,drying, or steaming and drying, being carried out continuously on atravelling conveyor belt. It is also possible to employ our process as asingle step in a combined bleaching operation such as a step in thecombined chlorine-peroxide bleaching methods known to the art.

Our process permits the bleaching of artificial fibers, especiallyregenerated cellulose and products manufactured therefrom by a rapid,simple and inexpensive method yielding uniformly satisfactory results.Mixed fibers, mixed fabrics, and similar materials may also be similarlyadvantageously treated in accordance with our process, since thehydrogen peroxide accumulatedon the cellulose artificial threads exertsa bleaching influence on the neighboring threads.

After the drying step it is sometimes desirable to permit the goods tostand in the air at room temperature, i. e. at a temperature ofapproximately 15 to 20 C. This after-step of standing may be prolongedif desired until any residual hydrogen peroxide which may remain in thefiber is decomposed. By suitably adjusting the concentration of thehydrogen peroxide solution by the addition of suitable agents it ispossible to regulate the bleaching action so that any desired bleachingeffect is secured. The liquid recovered from the fibrous material bysqueezing or centrifuging may, of course, be used over again in thebleaching of subsequent batches of fibers or fabrics.

As examples of our improved process for the bleaching of fibrousmaterials the following may be given.

Example I The fibrous material to be bleached is first passed through acontainer filled with dilute hydrogen peroxide solution The solutioncontained, per liter of solution:

Hydrogen peroxide (40% concentration by volume) cc 10 to 20 Ammoniumhydroxide. cc 1 to 2 Olein gram 0. 3 to 0. 5

After passing through the solution the fibrous material was squeezed orcentrifuged, and then dried in the air at ordinary room temperature, atemperature within the range 15 to 20 C. At the conclusion of thisprocess the fibrous material was bleached to a satisfactory white c010and the fiber had a soft smooth feel. I

Example II Fibrous material was first impregnated with a bleachingsolution, as in Example I, utilizing a solution of hydrogen peroxidewhich contained, per liter of solution:

Hydrogen peroxide (40% concentration by volume) cc 10 to 20 Ammoniumhydroxide cc 1 to 3 Sodium pyrophosphate crystals gram 1 Olein gram 0. 3to 0.5

The fibrous material to be bleached wasimpregnated with the bleachingliquor, as, in Example I, utilizing a bath of hydrogen peroxidecontaining per liter of solution:

Hydrogen peroxide (40% concentration by volume) cc 10 to 20 Ammoniawater cc 5 to 10 Sodium pyrophosphate cc 1 to 3 Olein gram 0. 3 to 0. 5

After squeezing out excess solution the fibrous material was conveyed ona conveyor belt through a drying apparatus and dried at temperatures ofapproximately'lS? C. The resulting product was bleached to asatisfactory white color and had a soft smooth feel.

Hydrogen peroxide (40% concentration by volume) cc 4 Disodium phosphatesgram 0. 3 Marseilles soap grams 3 After immersion, the artificial staplefiber was squeezed in order to free it from excess solution. It wassubsequently steamed for 20 minutes at a temperature of C. and thendried at a temperature of approximately 70 C. The pH value of thebleaching bath was 9.1 and the pH value of the artificial staple fibersafter the steaming treatment was 7.0. The fiber was bleached verysatisfactorily.

Example V 100 grams of artificial staple fiber prepared from cellulosewas immersed for 5 minutes in a bleaching bath constituted as follows:

Hydrogen peroxide (40% concentration by volume) cc Disodium phosphategram 0.

Borax grams Sufiicient water to make up 1 liter of solution.

Example VI 100 grams of artificial staple fiber prepared fromcellulosewas immersed for 5 minutes in a bleaching solution whichcontained in a liter of solution the following ingredients:

Hydrogen peroxide solution (40% concentration by volume) cc 5 Causticsoda grams 2 Monopotassium Buffer mixture{ phosphate grams 6.6

After immersion, the fiber was withdrawn and squeezed or centrifuged toremove excess liquor. It was then subjected to steaming and subsequentlydried as in Example IV. The pH value of the bleaching solution wasapproximately 7.7,

while the pH value of the artificial fibers, at the conclusion of thesteaming step, was 6.6. The goods were bleached to a satisfactory whitecolor.

Example VII Hydrogen peroxide of 40% by volume concentration; cc 3Sodium oxalate grams 4 After immersion, the goods were treated as inExample IV. The pH value of the bleaching solution when cold was 6.6.When heated to a temperature of substantially 100 C., the pH of thissolution became 9.0. No change in pH value of the artificial staplefiber occurred during the step of drying the fiber at the conclusion ofthe steaming process. The fibrous material was bleached to asatisfactory white color and had a soft smooth feel.

The foregoing details, procedures, temperatures, percentages and amountswhich have been given merely as illustrative of preferred modes in whichour improved process may be carried out are not to be regarded asrestrictive. term heat treatment, as it may be used in the specificationor claims, there should be understood either the treatment of the fibersto be bleached with the alkaline peroxide solution at substantially 100C. in the presence of steam, or in those instances where steam treatmentis not employed, the subjection of the fibers to the action of thealkaline bleaching solution at substantially 100 C. The subsequentdrying of the fibers is not to be considered as part of the heattreatment. Various changes may be made in such details of our process asdescribed which will nevertheless come within the purview of ourinvention. The scope of that invention is to be determined, not by theprocedures and amounts indicated as merely illustrative, but inaccordance with the scope of the appended claims.

We claim: 1. A process for bleaching artificial textile fiberscomprising the steps of impregnating the fibrous material with asolution containing a peroxygen compound, said solution being maintainedat a temperature of substantially 100 C., and then drying said fibrousmaterial at an elevated temperature within the range 50-90" C., the pHvalue of said fibrous material during said drying step being maintainedwithin the range 7.5 to 10 at the initial phase of said heat treatmentat substantially 100 C. and the pH value of said fibrous material duringsaid treatment at 100 C. falling within the pH range 6.0 to 7.6.

2. A process for bleaching artificial textile fibers, especially thoseprepared from regenerated cellulose such as artificial staple fiber,artificial silk and similar materials, which comprises the steps offirst impregnating the fibrous material with a solution of a peroxygencompound, removing said fibrous material from said solution, squeezingto remove excess liquid therefrom, drying said fibrous material at anelevated temperature within the range 90 to 100 C. and then continuingsaid drying step at lower temperatures, temperatures within thfiange 40to 70 C., the pH value of said materials being maintained below about8.0 during substantially said entire drying step.

3. A process as defined in claim 2 wherein the pH value of said fibrousmaterial duringsaid drying step is maintained within the range 6.0 to7.8.

4. A process for bleaching artificial textile fibers, especially textilefibers fashioned from regenerated cellulose and products made therefromsuch as artificial wool and artificial silk, which process comprises thesteps of impregnating the fibrous material with a solution of an activeoxygen-yielding compound, subjecting said impreg- By the 2,194.,ssa

nated fibrous material to the action of heat, and then drying saidimpregnated fibrous material, the pH value of said textile fibers beingmaintained on the alkaline side during the initial phase of said heattreatment of said impregnated fibers, and the pH value of said textilefibers at the conclusion of said heat treatment step being approximately7.0.

5. A process for bleaching artificial textile fibers, especially textilefibers fashioned from regenerated cellulose and products made therefromsuch as artificial wool and artificial silk, which process comprises thesteps of impregnating the fibrous material with a solution of hydrogenperoxide, subjecting said impregnated fibrous material to the action ofsteam, and then drying said fibrous material, the pH value of saidtextile fibers being maintained on the alkaline side during the initialphase of said steam treatment step, the pH value of said textile fibersat the end of said steam treatment being substantially equivalent tothat of a neutral solution.

6. A process for bleaching artificial textile fibers, more particularlytextile fibers fashioned from regenerated cellulose and products madetherefrom such as artificial wool and artificial silk, which processcomprises the steps of impregnating said fibrous material with asolution of hydrogen peroxide, subjecting said impregnated fibrousmaterial to the action of steam at a temperature of 100 C., and thendrying said fibrous material at a temperature within the range 50 to 90C., the pH value of said textile fibers being maintained within therange 7.5 to 10 during the initial phase of said steam treatment atsubstantially 100 C. and being maintained within the range 6.0 to 8.0during said step of steam treatment at substantially 100 C.

7. A process for bleaching artificial textile fibers, more particularlytextile fibers fashioned from regenerated cellulose and products madetherefrom such as artificial wool and artificial silk, which processcomprises the steps of impregnating the fibrous material with a solutionof hydrogen peroxide containing, as an alkalinizing agent, a salt of astrong base and a weak acid selected from the group which consists ofthe alkali metal pyrophosphates, disodium phosphate, borax, the alkalimetal succinates, the alkali metal malonates, and soap, subjecting saidimpregnated fibrous material to the action of heat, and then drying saidimpregnated fibrous material, the pH value of said textile fibers beingmaintained on the alkaline side during the initial phase of said heattreatment of said impregnated fibers.

8. A process as defined in claim 5 wherein a solution of hydrogenperoxide containing a butering agent for maintaining said solutionalkaline is utilized as the impregnating agent.

9. A process as defined in claim 5 wherein there ing a pH value below 7and containing an alkali metal oxalate, said solution becoming alkalinein reaction duringsaid subsequent heat treatment steps due to the actionof said alkali metal oxalate.

WILLI HUNDT. HERMANN BAIER.

is utilized a solution of hydrogen peroxide hav-

